The invention relates to a device useful for determining the discrete grip length of a fastener necessary for fastening together two or more pieces of material, such as sheet material. The invention is especially useful in the aircraft manufacturing or in the manufacture of other objects using rivets of different type and size in the construction.
As known in the art, many different types of fasteners are available for use. In the aircraft construction industry, one-piece rivets and two-piece fasteners such as high-lock, bimetal or huck fasteners are commonly used as well as other types of rivets, screws and bolts. The particular type, diameter and the length of fastener used in a particular connection depends upon several factors including the thickness or dimension of the stack. The diameter and type of fastener is usually selected according to the particular application and the forces, shear or tensile, to be exerted on the fastener. The length of fastener depends on the type, diameter and stack thickness.
For many types of fasteners, the manufacturer or the industry itself has developed charts correlating the stack thickness with the size and type of fastener to provide the length of fastener needed. In practice, the stack thickness is determined by manually measuring the dimension by either inserting a hand rule or gauge into the fastener hole or using a caliper, where the thickness of the pieces is accessible by caliper, and by visibly reading the dimension of the stack. The operator then consults the stack thickness chart, or other reference guide, and knowing the diameter and type of fastener to be used, obtains from the chart the discrete grip length of fastener needed for that particular hole. This procedure is time consuming and susceptible to human error in measuring the stack thickness or reading the stack thickness chart. The present invention reduces this chance of error and reduces the time required for determining the length of fastener needed by providing a device which measures the stack thickness through the hole and calculates from that measurement the discrete length of fastener needed according to the size and type of fastener selected.